#include <stdio.h>
int main()
{int x,y,day=0;
float m,sum=0,ave;
scanf("%f%d%d",m,x,y);
do {sum=sum+m*x;
day++;
x=x*2;}
while(x<=y);
ave=sum/day;
printf("average=%.2f\n",ave);
  return(0);
}
